Network switches, including for present purposes devices variously known as bridges. routers and brouters, may be connected to a variety of transmission media such as copper cable or optical fiber, using either a physical layer entity normally denoted PHY or a SERDES. These devices are usually external to the switching ASIC performing the basic functions of the network switch They employ a variety of interface protocols dependent upon the type of the cable and the port speed that is to say the design data rate at which data may be sent from or received by the port associated with the particular MAC. The most common type of interface protocols used at present are the IEEE TBI (10-bit interface) protocol used to connect to fiber cables rated for gigabit data rates and IEEE GMII 10-bit protocol which is used to connect the MAC to copper cable for gigabit Ethernet and the IEEE MII 5-bit protocol to connect the MAC to copper cable for {fraction (10/100)} Ethernet, that is to say Ethernet type data at either 10 or 100 megabits per second Recently other interfaces have been developed, such as the reduced gigabit media independent interface (RMGII) which supports a reduced 5-bit interface for PHYs supporting 1000/100/10 megabit per second Ethernet speeds on copper cable. At the same time a 5-bit reduced SERDES interface protocol has been agreed termed RTBI
SERDES devices for connection to fiber optic cable are different from PHYs used for connection to copper cable in that (assuming an 8-bit/10-bit encoding scheme) all the ten input and output pins of the SERDES carry data rather than the provision of some data bits and some control bits as in the GMII interface. The receiver side of the local snitches media access control device must be synchronised to the 10 bits of data from the transmitter block of the SERDES associated fifth the switch at the far end of the link Likewise the local switch's media access control transmitter block transmits 8-bit/10-bit encoded data to which the receiver of the SERDES at the far end of the link must be synchronised. As will be explained in more detail later there are a multiplicity of code groups. One character or symbol of importance to the present invention is an idle (I2) symbol which is made up of two code groups Several variations of the symbol exist. The receive sides of both the media access control device and the SERDES must decode and lock on to the idle symbols for communication to occur over a communication link
As swell as the recently defined RGMII and RTBI protocols various manufacturers have produced variants of SERDES devices to support both the TBI and RTBI protocols Various devices include interfaces relying on 10 bits or 5 bits using a single clock or two clocks on the receiver interface
It is generally desirable to be able to support a variety of interface protocols and to enable products to be modular in form enabling any configuration of the interfaces to be plugged into the ports of a network switch It is accordingly desirable to provide a means of identifying the SERDES device on the plug-in module in order that the software drivers for the media access control device can be correctly configured
It is known practice to identify a plug-in card be using either a memory-mapped register or a plug-in module which is readable by an on-board processor (CPU) by means of a series of encoded pins pulled high or low according to the deice attached. However, both these methods involve using pins on a module connector and impose a space or cost penalty A fully modular switch wherein all ports are of the plug-in type allotting support for testing a variety of different media types would add a substantial cost overhead to products